1. Field of the Invention
The present invention relates to an apparatus and method for determining rheological properties of biological and other liquids. The method and apparatus of the present invention is used to determine the viscosity and elastic properties of cervical mucus for women and other female mammals. For humans, the determination of the properties of the mucus is used to predict and indicate the inception and the presence of ovulation for increasing likelihood of conception or for contraception. For livestock and other mammals, the determination is used to detect estrus for breeding management.
2. Description of the Prior Art
Many forms of family planning require a woman wanting to avoid pregnancy to identify her fertile period so she can practice sexual abstinence or use other means of birth control during this period. On the other hand, marginally fertile couples desiring pregnancy have a higher probability of conceiving if sexual intercourse is confined to the female fertile period or if the couples abstain for several days before the period. Ovulation is the key event in the female fertile period. The fertile period consists of only about four days in the female menstrual cycle: three days preceding ovulation (necessitated by sperm survival), and one day after ovulation (necessitated by ovum survival).
It is well known that the rheology of cervical mucus undergoes significant changes at the onset and throughout the female fertile period. See Schuster, U.S. Pat. No. 3,982,423 (1976). During the immediate pre-ovulatory phase and the rest of the menstrual cycle, the mucus becomes less abundant and no longer possesses certain threadability characteristics. In rheological terms the mucus is highly viscous except during the ovulation phase of the menstrual cycle. If one can determine the changes in the viscoelastic properties of cervical mucus that occur before the onset of ovulation, it is possible to pinpoint the female fertile period.
In the so-called Billings method of contraception by periodic abstinence, a woman is taught to identify the precise characteristics of cervical mucus produced at various states of her menstrual cycle and their relationship to her fertile and infertile days. The method tends to be subjective and lacks quantitative precision so it tends to be unreliable. The more widely practiced Basal body temperature method uses the changes in daily temperature taken immediately at awakening to identify the temperature shift that occurs at or shortly after ovulation. To be effective the woman must adhere to a highly repetitive routine before the daily temperature taking because any restlessness, motion, infection or mental stress causes small temperature shifts, which can result in incorrect data. The Sympto-Thermal method charts temperature changes and changes in volume and viscosity of cervical mucus and teaches women to recognize such subjective symptoms of ovulation as intermenstrual pain. This method fares no better because the measurements lack precision and objectivity.
Kopito, U.S. Pat. No. 3,979,945 (1976) and the aforementioned Schuster patent both teach devices designed to give quantitative measurements of rheological properties of cervical mucus, but both are complex and difficult to use and are mechanical devices subject to error. The mucus is not tested in situ.
Detecting estrus in cattle is important but is difficult for the farmer. Failure to detect estrus at the proper time means delayed breeding and long calving intervals, which result in a decreased production of milk and beef. The problem is further complicated as herd size increases because it is difficult to observe more cows. Various techniques have been advanced for the detection of estrus in cattle. For example, Scott, U.S. Pat. No. 4,224,949 (1980), and McDougall, U.S. Pat. No. 3,844,276 (1974), tests electrical resistance of cervical mucus using a bovine vaginal probe. Rodrian, U.S. Pat. No. 4,247,758 (1981), measures movements of animals which are said to be increased during estrus. Zartman, U.S. Pat. No. 4,387,724 (1983), measures long-term deep body temperature. None of these techniques utilizes the changes in rheological parameters such as viscosity for bovine cervical mucus at the onset and throughout the bovine estrus period.